An erosion‐type hydrolysis behavior of insoluble protein fraction from Chlorella protothecoides

Abstract

BACKGROUND: Acid-induced hydrolysis of proteins has been used to improve the solubility and functional properties of various proteins, and could be a promising tool to facilitate the use of currently underutilized insoluble microalgae protein-rich fractions in food applications. However, the results of a prior study showed an unusual resistance of an insoluble microalgae protein-rich fraction to acid hydrolysis at room temperature.RESULTS: In the present study, the insoluble protein-rich fraction extracted from microalgae Chlorella prothothecoides was treated with 0.5 mol L −1 hydrochloric acid at 25, 45, 65 or 85 ∘ C for 0-4 h. The results showed that hydrolysis of the fraction at 85 ∘ C for 4 h led to decreases in the amount of insoluble protein-rich aggregates and the formation of fragments with a lower molecular weight, as well as an increase in protein solubility by approximately 40%. Nevertheless, some aggregated insoluble protein-rich particles remained, even after hydrolysis at 85 ∘ C for 4 h.CONCLUSION: The higher temperature improved the efficiency of the acid hydrolysis of the insoluble protein fraction from microalgae Chlorella prothothecoides, which is highly acid-resistant. Overall, an erosion-based mechanism was suggested for the acid hydrolysis of insoluble microalgae protein fraction.

Foaming of Acid-Hydrolyzed Insoluble Microalgae Proteins from Chlorella protothecoides

“…The insoluble microalgae protein fraction was extracted by a solvent (ethanol: acetone = 1: 1) after high-pressure treatment using a micro-fluidizer and fractionation using centrifugal separation according to a published method by Grossmann et al [20]. The extracted insoluble microalgae protein fraction was hydrolyzed at 65 or 85°C in 0.5 M HCl for 4 h, dialyzed and freeze-dried with modification according to Dai et al [2,21]. The untreated insoluble microalgae protein fraction contains 63.3 ± 2.9% protein with a solubility of 11.3 ± 0.1%; the protein content of Hydrolysates 65 and Hydrolysates 85 is 57.9 ± 0.1% and 55.3 ± 0.2% having solubility of 47.2 ± 0.7% and 63.3 ± 1.5%, respectively [22].…”

Behavior of concentrated emulsions prepared by acid‐hydrolyzed insoluble microalgae proteins from Chlorella protothecoides

“…The extracted insoluble microalgae protein fraction was then hydrolyzed at 65°C (Hydrolysates 65) or 85°C (Hydrolysates 85) in 0.5 mol L -1 HCl for 4 h. The hydrolysates were neutralized, dialyzed, and freeze dried prior using to prepare emulsions. 16 The characteristics of the extracted water-insoluble microalgae protein fraction and the two selected hydrolysates are listed in Supporting Information, Table S.1. 15 Miglyol 812, a medium-chain triglyceride blend was used as a model oil.…”

“…In comparison, Hydrolysates 85 are more intensively hydrolyzed to yield mostly soluble protein fragments with lower molecular weights resulting in smaller emulsion droplet size, which induces stronger interactions of emulsion droplet-droplet (packing) or / and proteins adsorbed at the surface of oil droplets. 15,16 The high overall viscosity of the emulsions (considering that only 3% protein was used in their manufacture) may also be explained by bridging. Bridging was identified as the primary cause for flocculation in dilute emulsions due to interfaces being heterogeneous in properties thereby providing docking and attachment sites on different droplets.…”

“…making it useful as an emulsifier. [14][15][16][17] Results from investigations of the behavior of moderately concentrated oil-in-water emulsion (with 10% w/w of a mediumchain triglycerides oil) stabilized by the microalgae insoluble protein fraction after hydrolyzing with 0.5 mol L -1 HCl at 85°C for 4 h (Hydrolysates 85) showed that emulsions were stable in terms of droplet size (at around 15 μm) after 14 days of storage, even when subjected to harsh environmental conditions such as an extreme pH (2)(3)(4)(5)(6)(7)(8)(9) or high salt concentrations (NaCl concentration 0-500 mmol L -1 or CaCl 2 concentration 0-50 mmol L -1 ), and no coalescence was observed. 14,17 However, visual and microscopic assessments revealed pronounced emulsion flocculation.…”